Four coordinated platinum and palladium complexes with geometrically distorted charge transfer state and their applications in light emitting devices

ABSTRACT

Described herein are platinum and palladium compounds with geometrically distorted charge transfer state, applications and methods for the preparation thereof. The platinum and/or palladium compounds described herein are capable of emitting light and can be used in light emitting devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 14/589,599, filed on Jan. 5, 2015, now allowed, which is a divisional of U.S. patent application Ser. No. 14/332,610, filed on Jul. 16, 2014, now U.S. Pat. No. 8,927,713, which is a divisional of U.S. patent application Ser. No. 13/399,252, filed on Feb. 17, 2012, now U.S. Pat. No. 8,927,713, which claims priority to U.S. Provisional Patent Application No. 61/444,387, filed on Feb. 18, 2011, all of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure relates to platinum and/or palladium complexes which are capable of emitting light and are thus useful as an emissive material in a device.

TECHNICAL BACKGROUND

Compounds capable of absorbing and/or emitting light are ideally suited for use in a wide variety of optical and electro-optical devices, including photo-absorbing devices such as solar- and photo-sensitive devices, photo-emitting devices, such as organic light emitting diodes (OLEDs), or devices capable of both photo-absorption and emission. Much research has been devoted to the discovery and optimization of organic and organometallic materials for use in optical and electro-optical devices. Generally, research in this area aims to accomplish a number of goals, including improvements in absorption and emission efficiency, as well as improvements in processing ability, among others.

Despite significant advances in research devoted to optical and electro-optical materials, many current devices comprising organic or organometallic materials have yet to be optimized. Many materials currently used in optical and electro-optical devices have a number of disadvantages, including poor processing ability, inefficient emission or absorption, and less than ideal stability, among others. Thus, a need exists for new materials which exhibit improved performance in optical and electro-optical devices. This need and other needs are satisfied by the present invention.

SUMMARY

The present invention relates to platinum, palladium or combination thereof complexes that exhibit photoemission, to methods of making such compounds, and to applications thereof, including optical devices comprising the compounds.

In one aspect, the compounds are represented by the formula:

wherein each of Ar1, Ar2, Ar3, and Ar4 comprise an aromatic ring or heterocyclic group comprising an atom X, Y, Z and W, respectively, coordinating to M atom by a linkage group, wherein each of the linkage groups comprise a carbon, nitrogen, halogen, sulfur, phosphor, oxygen, or a combination thereof, and wherein M atom is platinum, palladium or combination thereof.

In another aspect, the present disclosure provides a compound represented by the formula

wherein M is atom of platinum, palladium or combination thereof.

In another aspect, the present disclosure provides a compound represented by the formula

wherein M is atom of platinum, palladium or combination thereof.

In another aspect, the present disclosure provides a compound represented by the formula

wherein M is atom of platinum, palladium or combination thereof.

In other aspects, the present disclosure provides a light emitting device comprising at least one of the compounds described herein.

Also disclosed are optical devices, such as organic light emitting devices, photovoltaic devices (e.g., solar cells), and luminescent display devices that comprise one or more compounds of the invention as a functional material, such as a light-emitter or absorber, or both.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects and together with the description serve to explain the principles of the invention.

FIG. 1A illustrates chemical structures for Pt-001, Pt-008, and Pt-009 complexes, in accordance with various aspects of the present disclosure.

FIG. 1B illustrates DFT drawings of Pt-001 (left), Pt-008 (center), and Pt-009 (right) structures, in accordance with various aspects of the present disclosure.

FIG. 1C depicts structure drawings illustrating the lowest unoccupied molecular orbital (LUMO) for each of Pt-001 (left), Pt-008 (center), and Pt-009 (right), in accordance with various aspects of the present disclosure.

FIG. 1D depicts structure drawings illustrating the highest occupied molecular orbital (HOMO) for each of Pt-001 (left), Pt-008 (center), and Pt-009 (right), in accordance with various aspects of the present disclosure.

FIG. 2A illustrates the room temperature and 77K emission spectra of a Pt-001 complex, in accordance with various aspects of the present disclosure.

FIG. 2B illustrates the room temperature and 77K emission spectra of a Pt-008 complex, in accordance with various aspects of the present disclosure.

FIG. 2C illustrates the room temperature and 77K emission spectra of a Pt-009 complex, in accordance with various aspects of the present disclosure.

FIG. 3A is a plot of device efficiency vs. current density for an ITO/PEDOT:PSS/NPD (30 nm)/TAPC (10 nm)/Pt-008:mCpy (25 nm)/PO15 (20 nm)/LiF/Al device for Pt-008 ranging from 2 to 20%).

FIG. 3B illustrates the electroluminescent spectrum for an ITO/PEDOT:PSS/NPD (30 nm)/TAPC (10 nm)/Pt-008 (4%):mCPy (25 nm)/PO15 (20 nm)/LiF/Al device.

FIG. 4 is a drawing of a cross-section of an exemplary organic light-emitting diode (OLED).

Additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or can be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

DESCRIPTION

The present invention can be understood more readily by reference to the following detailed description of the invention and the Examples included therein.

Before the present compounds, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.

As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component” includes mixtures of two or more components.

Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.

It is also to be understood that if not described otherwise or specifically excluded all Pt atoms in the description of the inventive compounds can be substituted by Pd, or combination of Pt—Pd atoms.

The term “alkyl” as used herein is a branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. The alkyl group can be cyclic or acyclic. The alkyl group can be branched or unbranched. The alkyl group can also be substituted or unsubstituted. For example, the alkyl group can be substituted with one or more groups including, but not limited to, optionally substituted alkyl, cycloalkyl, alkoxy, amino, ether, halide, hydroxy, nitro, silyl, sulfo-oxo, or thiol, as described herein. A “lower alkyl” group is an alkyl group containing from one to six (e.g., from one to four) carbon atoms.

The terms “amine” or “amino” as used herein are represented by the formula NA¹A²A³, where A¹, A², and A³ can be, independently, hydrogen or optionally substituted alkyl, cycloalkyl, alkenyl, cycloalkenyl, alkynyl, cycloalkynyl, aryl, or heteroaryl group as described herein.

The term “halide” as used herein refers to the halogens fluorine, chlorine, bromine, and iodine.

The term “hydroxyl” as used herein is represented by the formula —OH.

The term “nitro” as used herein is represented by the formula —NO₂.

The term “nitrile” as used herein is represented by the formula —CN.

The term “thiol” as used herein is represented by the formula —SH.

Disclosed are the components to be used to prepare the compositions of the invention as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds cannot be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C-E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the invention. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the methods of the invention.

In one aspect, the present application discloses platinum and/or palladium complexes that can emit electromagnetic radiation. In another aspect, the emission of such inventive complexes can be tuned, for example, from the ultraviolet to near-infrared, by, for example, modifying the ligand structure. In another aspect, the inventive complexes can provide emission over a majority of the visible spectrum. In a specific example, the inventive complexes can emit light over a range of from about 400 nm to about 700 nm. In another aspect, the inventive complexes have improved stability and efficiency over traditional emission complexes. In yet another aspect, the inventive complexes can be useful as luminescent labels in, for example, bio-applications, anti-cancer agents, emitters in organic light emitting diodes (OLED), or a combination thereof. In another aspect, the inventive complexes can be useful in light emitting devices, such as, for example, compact fluorescent lamps (CFL), light emitting diodes (LED), incandescent lamps, and combinations thereof.

In one aspect, the inventive complex comprises a metal atom and a ligand. In another aspect, the ligand is a tridentate ligand and is attached to the metal atom with three ligands of the same or varying composition. In another aspect, the ligand is a tetradentate ligand. In another aspect, the metal atom comprises at least one of platinum, palladium, or an alloy or combination thereof. In one aspect, the metal atom is platinum. In another aspect, the metal atom is palladium.

In one aspect, the ligand comprises one or more of the following: a high triplet energy emitting ligand having a rigid structure, a donor-acceptor ligand having a distorted geometry, or a combination thereof. In one aspect, the complex comprises a high triplet energy emitting ligand having a rigid structure and a donor-acceptor ligand with a distorted geometry. In another aspect, any one or more ligands can be connected through a bridging ligand. The specific ligand, structure, and/or bridging ligand can vary as described herein, and one of skill in the art, in possession of this disclosure, could readily select appropriate ligands for a platinum and/or palladium complex.

In one aspect, the inventive complexes of the present disclosure can be represented by the general formula:

wherein each of Ar1, Ar2, Ar3, and Ar4 comprise an aromatic ring or heterocyclic group comprising an atom X, Y, Z and W, respectively, coordinating to a M atom by a linkage group, wherein each of the linkage groups comprise a carbon, nitrogen, halogen, sulfur, phosphor, oxygen, or a combination thereof, which can, in various aspects, be substituted and/or connected with each other, and wherein the M atom can comprise platinum, palladium or combination thereof.

In one aspect, the inventive complex an emitting component, such as, for example,

wherein M is atom of platinum, palladium or combination thereof.

In various aspects, the inventive complex can comprise the emitting component illustrated above, and a same or different donor-acceptor component. In one such aspect, the emitting component and the donor-acceptor component can form the following structure:

wherein M can comprise platinum (Pt-001), palladium, or combination thereof.

In another such aspect, the emitting component and the donor-acceptor component can form the following structure:

wherein M can comprise platinum (Pt-008), palladium, or combination thereof.

In yet another such aspect, the emitting component and the donor-acceptor component can form the following structure:

wherein M can comprise platinum (Pt-009), palladium, or combination thereof.

In one aspect, the use of a specific donor-acceptor component can create a unique distortion in the resulting complex. Each such distortion can provide an emission spectra having a unique shape or profile.

Thus, in one aspect, the specific emission spectra of a complex can be tuned by selecting appropriate donor-acceptor components. By then selecting one or more complexes having desired emission profiles, a lighting device can be created for an intended purpose. For example, a white OLED can be prepared using one or more inventive complexes of the present disclosure.

In various aspects, the inventive composition can be represented by one or more of the formulas illustrated herein. For any of the formulas illustrated in this disclosure, -A- can be represented by one or more of the following:

—U— can be represented by one or more of the following:

-Ph can be represented by one or more of the following:

—V— can be represented by one or more of the following

and -M- can be represented by Pt, Pd, or a combination thereof.

In another aspect, any recitation or illustration of:

in a structure can include compositions wherein the group comprises one or more of the following:

In yet another aspect, any recitation or illustration of:

in a structure can include compositions wherein the group comprises one or more of the following:

In yet another aspect, any recitation or illustration of:

in a structure can include compositions wherein the group comprises one or more of the following:

In various aspects, specific non-limiting examples of the inventive composition can be represented by one or more of the following formulas:

In another aspect, the inventive complex the inventive complex can be represented by one or more of the following:

In yet another aspect, the inventive complex can be represented by one or more of the following:

In another aspect, the inventive complex is a platinum complex comprising one or more of the following formulas:

In another aspect, the inventive complex is a platinum complex comprising one or more of the following formulas:

In another aspect, the inventive complex is a platinum complex comprising one or more of the following formulas:

In another aspect, the inventive complex is a platinum complex comprising one or more of the following formulas:

In another aspect, the above compounds comprise a palladium atom as a metal center.

In another aspect, the inventive complex is not any one or more of the compounds described or illustrated herein. In an exemplary aspect, the inventive complex is not:

The above exemplary aspect is not intended to be limiting, but instead representative of aspects wherein any one or a combination of compounds described or illustrated herein are excluded from the invention.

The inventive complexes can be prepared using conventional chemical synthesis techniques. Several synthetic schemes are illustrated herein, but the invention is not intended to be limited to the recited schemes. Temperatures, catalysts, concentrations, reactant compositions, and other process conditions can vary, and one of skill in the art, in possession of this disclosure, could readily select appropriate reactants and conditions for a desired complex.

In one aspect, a complex, such as, for example, a Pt-001 complex, can be prepared by first preparing a 3-(pyridine-2-yloxy)phenol. This species can then be reacted to form 2-(3-(3-bromophenoxy)phenoxy)pyridine, which can be further reacted to form 2-(3-(3-(3,5-dimethyl-1H-pyrazol-1-yl)phenoxy)phenoxy)pyridine. This species can then be reacted to form the Pt-001 complex.

In another aspect, a Pt-008 complex can be prepared according to the following scheme.

In yet another aspect, a Pt-009 complex can be prepared according to the following scheme:

In another aspect Pd compounds can be prepared accordingly to schemes described herein.

The compounds of the invention are useful in a variety of optical applications. As light emitting materials, the compounds can be useful in organic light emitting diodes (OLED s), luminescent devices and displays, and other light emitting devices. The emission (and absorption) profile of the compounds can be tuned by varying the structure of the ligand surrounding the metal center. For example, compounds having a ligand with electron withdrawing substituents will generally exhibit different optical properties, including emission and absorption, than compounds having a ligand with electron donating substituents. Generally, a chemical structural change affects the electronic structure of the compound, which thereby affects the absorption and emission of the compound. Thus, the compounds of the present invention can be tailored or tuned to a specific application that desires a particular emission or absorption characteristic.

In one embodiment, the compounds can be used in an OLED. FIG. 4 shows a cross-sectional view of an OLED 100, which includes substrate 102 with an anode 104, which is typically a transparent material, such as indium tin oxide, a layer of hole-transporting material(s) (HTL) 106, a layer of light processing material 108, such as an emissive material (EML) including an emitter and a host, a layer of electron-transporting material(s) (ETL) 110, and a metal cathode layer 112.

In one aspect, a light emitting device, such as, for example, an OLED, can comprise one or more layers. In various aspects, any of the one or more layers can comprise indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonate (PSS), N,N′-di-1-naphthyl-N,N′-diphenyl-1,1′-biphenyl-4,4′diamine (NPD), 1,1-bis((di-4-tolylamino)phenyl) cyclohexane (TAPC), 2,6-Bis(N-carbazolyl)pyridine (mCpy), 2,8-bis(diphenylphosphoryl)dibenzothiophene (PO15), LiF, Al, or a combination thereof.

In this embodiment, the layer of light processing material 108 can comprise one or more compounds of the present invention optionally together with a host material. The host material can be any suitable host material known in the art. The emission color of an OLED is determined by the emission energy (optical energy gap) of the light processing material 108, which as discussed above can be tuned by tuning the electronic structure of the emitting compounds and/or the host material. Both the hole-transporting material in the HTL layer 106 and the electron-transporting material(s) in the ETL layer 110 can comprise any suitable hole-transporter known in the art. A selection of which is well within the purview of those skilled in the art.

It will be apparent that the compounds of the present invention can exhibit phosphorescence. Phosphorescent OLEDs (i.e., OLEDs with phosphorescent emitters) typically have higher device efficiencies than other OLEDs, such as fluorescent OLEDs. Light emitting devices based on electrophosphorescent emitters are described in more detail in WO2000/070655 to Baldo et al., which is incorporated herein by this reference for its teaching of OLEDs, and in particular phosphorescent OLEDs.

EXAMPLES

The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compounds, compositions, articles, devices and/or methods claimed herein are made and evaluated, and are intended to be purely exemplary of the invention and are not intended to limit the scope of what the inventors regard as their invention. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ° C. or is at ambient temperature, and pressure is at or near atmospheric. Unless indicated otherwise, in all examples described herein, Pt and/or Pd atoms can be used in each other's place, such that both aspects comprising Pt and aspects comprising Pd are disclosed.

Example 1: Pt-001

In a first example, a Pt-001 complex, as described herein, was synthesized. Initially, 3-(pyridine-2-yloxy)phenol was synthesized. Under a nitrogen atmosphere, a pressure vessel was charged with a magnetic stir bar, resorcinol (110 mmol), 2-bromopyridine (100 mmol), 1-methylimidazole (5 mmol), and potassium carbonate (200 mmol). Pyridine (80 mL) was added and bubbled with nitrogen for 20 minutes before copper(I) iodide (10 mmol) was added and bubbled 10 minutes further. The vessel was sealed and heated to 140° C. while stirring. After 2 days, the solution was allowed to cool. The solids were then filtered off and rinsed with a 50:50 mixture of toluene and methanol. The filtrate was reduced by rotary evaporation and 150 ml of water containing 10 mL glacial acetic acid was added and shaken vigorously. The water was decanted off and 50 mL of DCM was added, forming an off white precipitate which was collected by vacuum filtration and dried with ether, resulting in the pure product 3-(pyridin-2-yloxy)phenol with a 55% yield.

In another step, 2-(3-(3-bromophenoxy)phenoxy)pyridine was synthesized. Under a nitrogen atmosphere, a pressure vessel was charged with a magnetic stir bar, 3-(pyridin-2-yloxy)phenol (50 mmol) as produced above, 2,6-dibromopyridine (50 mmol), 1-methylimidazole (25 mmol), and potassium carbonate (100 mmol). Toluene (80 mL) was added and bubbled with nitrogen for 20 minutes before copper(I) iodide (5 mmol) was added and the solution bubbled for 10 minutes further. The vessel was sealed and heated to 140° C. while stirring. After 2 days, the solution was allowed to cool and the solids were filtered off and rinsed with dichloromethane. The filtrate was added to a separatory funnel containing DCM and water. The water phase was washed 3 times with 75 mL DCM, and the combined organic layers were washed once with pure water. The organic layer was then collected, dried with magnesium sulfate, filtered, and the filtrate reduced by rotary evaporation. The resulting oil was purified by column chromatography using DCM over silica resulting in the pure product 2-(3-(3-bromophenoxy)phenoxy)pyridine with a 60% yield. ¹H NMR (CDCl₃): 6.80-6.85 (m, 2H), 6.91 (s, 1H), 6.94 (s, 1H), 6.97-7.03 (m, 2H), 7.19 (vt, 1H), 7.21-7.24 (m, 2H), 7.36 (vt, 1H), 7.70 (dd, 1H), 8.21 (dd, 1H).

In another step, 2-(3-(3-(3,5-dimethyl-1H-pyrazol-1-yl)phenoxy)phenoxy)pyridine was synthesized. After standard cycles of evacuation and back-fill with dry and pure nitrogen, an oven-dried Schlenk flask equipped with a magnetic stir bar was charged with Cu₂O (1 mmol, 10 mol %), syn-2-pyridinealdoxime (4 mmol, 20 mol %), 3,5-dimethylpyrazole (12 mmol), Cs₂CO₃ (25 mmol), 2-(3-(3-(3,5-dimethyl-1H-pyrazol-1-yl)phenoxy)phenoxy)pyridine (10 mmol), and anhydrous, degassed acetonitrile (100 mL). The solution was refluxed for 2 days, allowed to cool to room temperature, diluted with dichloromethane, and filtered through a plug of Celite. The filter cake was washed with dichloromethane (100 mL) and the filtrate was concentrated under vacuo to yield a residue, which was purified by column chromatography on silica gel to obtain the pure product 2-(3-(3-(3,5-dimethyl-1H-pyrazol-1-yl)phenoxy)phenoxy)pyridine in 45% yield. ¹H NMR (CDCl₃): 2.29 (s, 3H), 2.28 (s, 3H), 5.98 (s, 1H), 6.84 (vt, 1H), 6.85-6.93 (m, 3H), 6.98-7.04 (m, 2H), 7.13 (vt, 1H), 7.19 (dd, 1H), 7.35 (vt, 1H), 7.39 (vt, 1H), 7.69 (dd, 1H), 8.19 (dd, 1H).

In another step, the Pt-001 complex was synthesized. A mixture of 2-(3-(3-(3,5-dimethyl-1H-pyrazol-1-yl)phenoxy)phenoxy)pyridine (1 mmol), K₂PtCl₄ (0.41 mg, 1 mmol), and acetic acid (35 mL) was refluxed for 3 days. The mixture was allowed to cool to room temperature. The resulting white complex was filtered off and washed with H₂O, cold MeOH, and Et₂O, and dried under vacuum to produce Pt-001 in 60% yield. The compound was sublimed under vacuum over a four zone gradient of 220° C.-190° C.-150° C.-110° C. and collected with a 65% yield. ¹H NMR (CDCl₃): 2.23 (s, 3H), 2.70 (s, 3H), 6.09 (s, 1H), 6.93 (dd, 1H), 7.01 (vt, 1H), 7.03-7.11 (m, 3H), 7.14 (d, 1H), 7.17 (vt, 1H), 7.37 (d, 1H), 7.88 (dd, 1H), 8.80 (d, 1H).

Example 2: Pt-008

In a second example, a Pt-008 complex, as described herein, was synthesized according to the following scheme:

Initially, 2-tetrahydropyranyloxycarbazole was synthesized. To a solution of 2-hydrocarbanzole (2.7 g, 15 mmol) and PPTS (38 mg, 0.15 mmol) in DCM (150 mL) was added dropwise with 3,4-Dihydro-2H-pyran (1.4 mL, 15 mmol) in 10 minutes, and the mixture was stirred at 0° C. over night, which was monitored with TLC. The insoluble 2-hydrocarbanzole remained was then removed with filtration, and the solution was concentrated. The desired product was purified through an silica gel chromatography with hexane/ethyl acetate=10:1 as eluent. (0.7 g, white solid, 17% yield) ¹H NMR (CDCl₃): 1.58-1.77 (m, 3H), 1.88-1.93 (m, 2H), 1.99-2.10 (m, 1H), 3.60-3.67 (m, 1H), 3.90-4.03 (m, 1H), 5.49 (t, J=3.1 Hz, 1H), 6.95 (dd, J₁=8.6 Hz, J₂=2.1 Hz), 7.13 (d, J=2.4, 1H), 7.16-7.21 (m, 1H), 7.30-7.38 (m, 2H), 7.90-7.98 (m, 3H).

In another step, N-[3-(3,5-Dimethylpyrazolylphenyl)]-2-tetrahydropyranyloxycarbazole was synthesized. To a 25 mL sealed tube was added with 2-Tetrahydropyranyloxycarbazole (380 mg, 1.42 mmol), N-(3-Iodophenyl)-3,5-dimethylpyrazole (430 mg, 1.45 mmol), potassium carbonate (415 mg, 3 mmol), copper(I) iodide (28 mg, 0.15 mmol), L-proline (35 mg, 0.3 mmol) and DMSO (5 mL) in glove box, and the mixture was stirred at 90° C. for 2 days. After cooling to rt, the mixture was treated with water (50 mL) and ethyl acetate (30 mL), and the water phase was extracted with ethyl acetate (3×20 mL). The organic extracted phase was combined, washed with brine (3×20 mL), dried with magnesium sulfate and concentrated. The resulting crud product was purified with an silica gel chromatography with hexane/ethyl acetate=5:1 as eluent to give an brown viscous solid. (460 mg, 74% yield).

In another step, N-(3,5-Dimethylpyrazolylphenyl)-2-hydroxycarbazole was synthesized. To a 100 mL round flask was added with the solution of N-[3-(3,5-Dimethylpyrazolylphenyl)]-2-tetrahydropyranyloxycarbazole (330 mg, 0.75 mmol) and PPTS (1 mg) in ethyl acetate (50 mL), and the mixture was kept at 50° C. for 24 hours. After cooling, the resulting product was directly treated with an flash column using hexane/ethyl acetate=3:1 as eluent to give N-(3,5-Dimethylpyrazolyl-phenyl)-2-hydroxycarbazole as a white solid. (230 mg, 87% yield).

In another step, N-[3-(3,5-Dimethylpyrazolyl)phenyl]-2-(pyridinyl-2-oxy)carbazole was synthesized. To a 25 mL sealed tube in glove box was added with N-(3,5-Dimethylpyrazolylphenyl)-2-hydroxycarbazole (210 mg, 0.60 mmol), 2-bromopydine (0.1 mL, 0.9 mmol), 1-methylimidazole (24 μL, 0.9 mmol), potassium carbonate (166 mg, 1.2 mmol), copper(I) iodide (12 mg, 0.06 mmol) and toluene (2 mL), and the mixture was heated at 120° C. for 3 days. After cooling to rt, the mixture was treated with water (50 mL) and ethyl acetate (30 mL), and the water phase was extracted with ethyl acetate (3×20 mL). The organic extracted phase was combined, washed with brine (3×20 mL), dried with magnesium sulfate and concentrated. Further purification of chromatography gave the product as a clear gel solid. (0.20 g, 77% yield).

In another step, the Pt-008 complex, as described herein was synthesized. To a 25 mL sealed tube in glove box was added with N-[3-(3,5-Dimethylpyrazolyl) phenyl]-2-(pyridinyl-2-oxy)carbazole (80 mg, 0.17 mmol), potassium tetrachloro-platinate (70.6 mg, 0.17 mmol) and acetic acid (3 mL), and the mixture was heated at 120° C. for 3 days after bubbled for 15 minutes. After cooling to room temperature, the resulting solution was treated with water (15 mL), and a dash solid was precipitated out. The solid was collected and purified with a flash neutral aluminum oxide column using hexane/DCM=1:1 as an eluent to give a complex as gray solid. (25 mg, 23% yield) ¹H NMR (d⁶-DMSO): 2.21 (s, 3H), 2.71 (s, 3H), 5.72 (s, 1H), 6.37 (s, 1H), 7.16 (d, J=12.0, 1H), 7.23-7.29 (m, 2H), 7.33-7.45 (m, 3H), 7.55 (d, J=8.0, 1H), 7.91 (d, J=8.0, 1H), 7.99 (d, J=8.0, 1H), 8.10-8.16 (m, 1H), 8.17 (d, J=8.0, 1H), 8.28 (d, J=8.0, 1H), 8.82 (d, J=5.6, 1H). The reaction was then scaled to get 100 mg Pt-008, which give 30 mg crystallized Pt-008 after sublimation.

Example 3: Pt-009

In a third example, a Pt-009 complex, as described herein, was synthesized according to the following scheme:

Initially, N-tetrahydropyranyl-2-tetrahydropyranyloxy-carbazole was synthesized. To a solution of 2-hydrocarbanzole (2.7 g, 15 mmol) and PPTS (38 mg, 0.15 mmol) in DCM (150 mL) was added dropwise with 3,4-Dihydro-2H-pyran (5 mL, 54 mmol) in 10 minutes, and the mixture was stirred at rt for 16 hours, which was monitored with TLC. The clear solution was concentrated. The desired product was purified through an silica gel chromatography with hexane/ethyl acetate=10:1 as eluent. (5.1 g, white solid, 96% yield).

In another step, N-tetrahydropyranyl-2-hydroxycarbazole was synthesized. To a 250 mL round flask was added with the solution of N-tetrahydropyranyl-2-tetrahydro-pyranyloxy-carbazole (1.77 g, 5.0 mmol) and PTSA (10 mg, 0.05 mmol) in ethyl acetate (100 mL), and the mixture was kept at rt over night. TLC showed that most of the disubstituted carbazole was transferred, and trace sodium bicarbonate was slowly added into the system to quench the reaction. The volatiles ware removed in vacuum, and the resulting product was treated with an usual work-up procedure. Flashing silica gel chromatography using hexane/ethyl acetate=5:1 as eluent to give 2-[3-(3,5-Dimethylpyrazol-1-yl)-phenoxy]-carbazole as a white solid. (1.06 g, 79% yield).

In another step, 2-[3-(3,5-Dimethylpyrazol-1-yl)-phenoxy]-N-(tetrahydropyranyl) carbazole was synthesized. To a 100 mL sealed tube was added with N-tetrahydropyranyl-2-hydroxycarbazole (880 mg, 3.0 mmol), N-(3-Bromophenyl)-3,5-dimethylpyrazole (826 mg, 3.30 mmol), Cesium carbonate (2.9 g, 3 mmol), copper(I) iodide (57 mg, 0.3 mmol), N, N-dimethylglycine (93 mg, 0.9 mmol) and 1,4-dioxane (8 mL) in glove box, and the mixture was stirred at 90° C. for 3 days. After cooling to rt, the mixture was treated with water (75 mL) and ethyl acetate (40 mL), and the water phase was extracted with ethyl acetate (3×30 mL). The organic extracted phase was combined, washed with brine (3×30 mL), dried with magnesium sulfate and concentrated. The resulting crude product was purified with an silica gel chromatography with hexane/ethyl acetate=3:1 as eluent to give an white colloidal solid. (1.12 g, 79% yield).

In another step, 2-[3-(3,5-Dimethylpyrazol-1-yl)-phenoxy]-carbazole was synthesized. To a 50 mL round flask was added with the solution of 2-[3-(3,5-Dimethylpyrazol-1-yl)-phenoxy]-N-(tetrahydropyranyl)carbazole (0.49 g, 1.12 mmol) and MsOH (0.36 mL, 5.6 mmol) in methanol (20 mL), and the mixture was kept at rt for 30 minutes then 50° C. for 1.5 hours. TLC showed that all the protected starting material was transferred, and then trace sodium bicarbonate was added into the system to quench the reaction. The resulting product was directly treated with an flash column using hexane/ethyl acetate=3:1 as eluent to give N-tetrahydropyranyl-2-hydroxycarbazole as a white solid. (0.32 g, 81% yield).

In another step, 2-[3-(3,5-Dimethylpyrazol-1-yl)-phenoxy]-9-pyridin-2-ylcarbazole was synthesized. To a 25 mL sealed tube in glove box was added with 2-[3-(3,5-Dimethylpyrazol-1-yl)-phenoxy]-carbazole (450 mg, 1.27 mmol), 2-bromopydine (0.41 mL, 3.82 mmol), 1-methylimidazole (0.05 mL, 0.64 mmol), potassium carbonate (351 mg, 2.54 mmol), copper(I) iodide (25 mg, 0.13 mmol) and toluene (10 mL), and the mixture was heated at 120° C. for 3 days. After cooling to rt, the mixture was treated with water (50 mL) and ethyl acetate (30 mL), and the water phase was extracted with ethyl acetate (3×20 mL). The organic extracted phase was combined, washed with brine (3×20 mL), dried with magnesium sulfate and concentrated. The crude product was further purified with chromatography to give a clear gel solid. (520 mgg, 95% yield).

In another step, the Pt-009 complex, as described herein, was synthesized. To a 100 mL sealed tube in glove box was added with 2-[3-(3,5-Dimethylpyrazol-1-yl)-phenoxy]-9-pyridin-2-ylcarbazole (520 mg, 1.21 mmol), potassium tetrachloro-platinate (552 mg, 1.33 mmol) and acetic acid (25 mL), and the mixture was heated at 110° C. for 3 days after bubbled for 15 minutes. After cooling to rt, the resulting solution was treated with water (70 mL), and a dash solid was precipitated out. The solid was collected and purified with a flash neutral aluminum oxide column using DCM as an eluent to give a complex as gray solid. (370 mg, 47% yield) Further purification by sublimation give 100 mg crystallized solid of Pt-009. ¹H NMR (CDCl₃): 1.58-1.77 (m, 3H), 1.88-1.93 (m, 2H), 1.99-2.10 (m, 1H), 3.60-3.67 (m, 1H), 3.90-4.03 (m, 1H), 5.49 (t, J=3.1 Hz, 1H), 6.95 (dd, J₁=8.6 Hz, J₂=2.1 Hz), 7.13 (d, J=2.4, 1H), 7.16-7.21 (m, 1H), 7.30-7.38 (m, 2H), 7.90-7.98 (m, 3H). 

What is claimed is:
 1. A compound represented by one of the following formula:

wherein M is platinum or palladium;

V is N or C; U is N or a group comprising C; and A is O, N, or a group comprising C or Si.
 2. The compound of claim 1, wherein the compound is a compound of formula:


3. The compound of claim 1, wherein the compound is a compound of formula:


4. The compound of claim 1, wherein the compound is a compound of formula:


5. The compound of claim 1, wherein the compound is a compound of formula:


6. The compound of claim 1, wherein the compound is a compound of formula:


7. The compound of claim 1, wherein the compound is a compound of formula:


8. The compound of claim 1, wherein the compound is a compound of formula:


9. The compound of claim 1, wherein the compound is a compound of formula:


10. The compound of claim 1, wherein V is N.
 11. The compound of claim 1, wherein U is N.
 12. The compound of claim 1, wherein A is O.
 13. The compound of claim 1, wherein


14. A light emitting device comprising the compound of claim
 1. 15. An OLED device comprising the compound of claim
 1. 16. The OLED device of claim 15, wherein the device is a phosphorescent OLED device.
 17. A photovoltaic device comprising the compound of claim
 1. 